PM motors are used in electric vehicles and others. In many cases, it is requested to implement an inverter control system by a sensor-less system for driving a PM motor. As a sensor-less system, an analogue filter system is known which estimates a magnetic pole position of a PM motor on a basis of an internal induced voltage of the PM motor (see non-patent document 1, for example).
FIG. 6 shows an example of configuration of an inverter device (current source inverter device) based on sensor-less control depending on the internal induced voltage. This inverter device 10 includes a direct current power supply not shown, a 120-degree conduction inverter 2, a voltage sensor 3, a PM motor 4, an integrator circuit 5, and a logic conversion circuit 6. The voltage and current of the direct current power supply which are supplied to 120-degree conduction inverter 2 are represented by Vdc and Idc, respectively.
Integrator circuit 5 is configured to convert a terminal voltage “V” of PM motor 4, which is sensed by voltage sensor 3, to magnetic pole information by calculating an internal induced voltage “e” of PM motor 4 on a basis of terminal voltage V, and integrating the terminal voltage V.
Logic conversion circuit 6 is configured to receive input of an output of integrator circuit 5, and generate a current having a 120-degree conduction pattern synchronized with internal induced voltage e of PM motor 4 by using a logic circuit, and supply same to 120-degree conduction inverter 2.
The system shown in FIG. 6, which constitutes a control loop, may obtain phase information different from the phase of the internal induced voltage under the influence of the inductance of PM motor 4 at high load. If the power factor is controlled with this error in phase due to the inductance, the power factor falls from a desired power factor because of the error in measurement, which adversely affects the efficiency of operation.
In order to improve the power factor, a method is disclosed in which a delay processing circuit 7 is provided between integrator circuit 5 and logic conversion circuit 6 in inverter device 1 shown in FIG. 7 (see non-patent document 2, for example).
Delay processing circuit 7 is configured to delay by a predetermined amount the phase of the current having a 120-degree conduction pattern generated by logic conversion circuit 6.